The dual in-line package (DIP) is the standard carrier for integrated circuits (IC's) in current electronic circuit practice. The DIP comprises a rigid housing, generally of insulating plastic, which surrounds the IC and protects it from mechanical, chemical, and electrical hazards, and a set of leads or pins which are connected electrically to contacts on the IC chip before the package is sealed and which function externally to connect the package electrically and mechanically to balance-of-circuit components. IC's come in one of several standard regular sizes with relatively standardized numbers of connector pins, e.g., 8, 12, 16, 24, 32. For a given configuration, the pin size and the spacing between pins is also standardized.
In normal practice, DIP IC's are installed onto printed circuit boards to form an electronic assembly in one of two ways: 1) the DIP IC connector pins are inserted into holes proformed in or drilled through a printed circuit board and the DIP IC pins are hard-soldered to metal tracks on the printed circuit board, thus making electrical connection and providing a mechanically secure installation; or 2) a socket is soldered onto the printed circuit board and the DIP IC leads are inserted into the socket and are retained by friction. This arrangement permits easy replacement of the IC. In either method of installation, portions of the DIP leads along the sides of the housing are electrically exposed, allowing for external electrical contact for such purposes as testing and troubleshooting.
There is frequent call for troubleshooting of electronic circuit boards carrying DIP IC's. Swapping a suspected bad DIP IC is a well known way to check functioning of an individual component. Swapping, however, is not physically feasible if the DIP is hard soldered to the circuit board. For socket mounted DIP IC's, on the other hand, swapping is not economically feasible except when the number of different IC's in use is very limited. In most instances, the number of different spare IC's which would have to be kept on-hand to implement swapping as a standard troubleshooting strategy would necessitate maintenance of a prohibitively large and expensive inventory of spare chips.
The preferred method of troubleshooting is electronic measurement at various points in a circuit. By measuring the inputs and outputs of a DIP IC, a technician can determine if its performance is satisfactory. The technician therefore must be able to make signal and voltage measurements on specific leads of individual components. Performing measurements on individual DIP IC pins is often required to isolate trouble in a circuit to a particular section of a circuit board or a specific chip and is indispensable for diagnosing faults in individual IC's.
The simplest and most common currently available device for electrical access to the pins on a DIP IC is the prior art DIP test clip shown in FIG. 1. The standard DIP test clip now in use is mechanically analogous to a simple alligator clip.
In use, the test clip is placed over a DIP IC which is attached to a circuit board. One end of the test clip, fitted with contact surfaces separated from one another by insulation to avoid shorting, makes contact with the IC leads. The other end has pin extensions which provide access for connecting test probes to the extensions of the pins protruding out the top of the test clip. The clip is held in place by spring pressure.
An inherent problem with the standard test clip of this type is that the very small typical separation of adjacent test pin ends (0.065 inches) protruding from the top of the test clip, as shown in FIG. 1, creates a significant risk of accidental shorting of adjacent pins. There are several types of test probes currently in use for performing measurements on energized circuits which are typically used in conjunction with DIP test clips. The most common are (1) the minigrabber, (2) the minigator clip, (3) the oscilloscope probe. The minigrabber has a typical contact width of 0.09 in., the minigator clip has a typical nose width of 0.13 in., and the oscilloscope probe has a typical contact width of 0.09 in., all significantly larger than the standard separation of the pins in a test clip. In addition, the minigator clip can short to the adjacent pin even after it has been securely connected to the test clip pin if the probe wire attached to it is accidentally moved.
If adjacent pins are shorted the IC will often be destroyed, preventing further troubleshooting efforts until a replacement IC can be obtained and inserted. Thus, for all of the test probes used in conjunction with present DIP test clips, the circuit under investigation must be deenergized each time a new test point is to be measured and great care must be taken so that accidental movement of the test leads does not result in shorting to adjacent pins. The deenergization of circuitry while moving test probes even in low voltage circuits is presently considered good troubleshooting practice because of the high likelihood of shorting.
During normal troubleshooting activities for DIP IC's, however, only a few pins on a particular IC are really of interest to the technician. The key limitation of the current test clip is the presence of pins not of interest, creating the likelihood of shorting and the need to deenergize circuits between tests. Thus there is need for an improvement which eliminates much of the risk of shorting and the concomitant inconvenience and time loss due to the need to deenergize the circuit to move a probe during testing or troubleshooting. The current invention satisfies this need.